Molded indurated-fiber articles and process op making same



Gil

Patented June 11, 1929.

UNITED STATES 1,717,092 PATENT OFFICE.

HORACE H. CLARK, OF FARHINGDALL E, NEW JERSEY, ASSIGNOBTO CLARK FIBRE PRODUCTS CORPORATION, A CORPORATION OF DELAWARE.

MOLDED INDUBATED-FIBER ARTICLES AND PROCE8$ OI MAKING SAME.

No Drawing. Application filed January 15, 1927, Serial No. 181,460, and in France June 4, 1926.

This invention relates to the manufacture of boxes, cups or similar articles out of integral masses of cellulose material of the type commonly called indurated fiber or vulcanized fiber.

By these terms is meant a material heretofore usually made out of sheets of paper which, after being separately saturated with a zinc chloride solution, have been placed one on top of another and pressed together in a pile, or rolled up together in a spiral to form a tube which is consolidated by pressure, and finally dried or cured after the zinc chloride has been washed out in successive baths of progressively weaker solutions, ending with a washing in fresh water.

So far as I know this material has never been made otherwise than in this built-up, i. e. originally laminated form. That s to say it has never been possible to make artlcles at least not such as have any considerable thickness of walls) by molding a mass of the cellulose pulp directly into the desired final form, and then saturating it with the zinc chloride, or equivalent induratin solution, and finally washing and drying it as above described.

The principal reason why this direct molding process has not been followed heretofore has been because the indurating solution (zinc chloride, or its equivalent) has not penctrated more than about fifteen or twenty thousandths (.015 or .020) of an inch below the surface of the dried pulp. Consequently, if the mass to be indurated was more than thirty or 'forty'thousandths (.030 or .040) of an inch thick, there was always left an inner core of fiber never reached by the zinc chloride, and consequently never indurated, no matter how long the mass was left submerged in the bath. As the material shrinks about 25% in thickness on drying, after treatment with the zinc chloride or other indurating solution as above described,

this has heretofore fixed a limit of about nal pulp from the cellulose ber, and subject.

ing the molded blank to compression before induration, this limit of depth of penetration by the zinc chloride in the indurating process can be greatly increased, so that it then becomes possible to mold the pulp into final forms which will have sufiicient thickness of wall after induration to give them the needed strength. As aresult I am able to produce-integrally molded articles of indurated fiber havin walls of an eighth of an inch and more in t llCkIlBSS, or more than four times the thickness previously possible.

' I accomplish this by increasing the capacity-of the original dried pulp to uniformly absorb the indurating fluid. The reason (as I believe) why the zinc chloride did not formerly penetrate the dried pulp sheet or blank to a depth of more than about .015 of an inch was traceable to two causes. In the first place, the pul was not sufficiently freed .from gums, an similar impurities of a relatively non-absorbent character, in the usual process of making paper pulp to render it sufficiently hygroscopic. In the second place, an ordinary molded blank of paper pulp has more or less air spaces in its interior. The indurating fluid is so heavy and has such surface tension that after it has penetrated the first few thousandths of an inch from the exterior surfaces of the blank it forms therewith airtight films which hermetically seal the air trapped in the unreached cavities of the remaining, inner portion of the blanks wall, and thereafter the increasing resistance to compression of said trapped air soon checks further inward flow of said indurating solution. I have discovered that if in the original pulp making process, the fiber is cooked sufiiciently longer,'or in a sufliciently stronger solution, or both, or under sufliciently increased pressure, the subsequently dried pulp can be rendered so free from such impurities, which are dissolved outlby this treatment, that it becomes vastly more hygroscopic and absorbent, and then will much more readily and completely absorb the indurating solution and so allow it to penetrate to greater depths. Also, if the walls of the blank originally molded from such pulp are, before induration, subjected to suitable pressure, as in preliminary forming dies, all air cells therein will be collapsed, and their contained air expelled, so that no trapped air is left to halt the inward progress of the in durating fluid. When th1s is accom lished, all that remains necessary to produce irectly molded articles is the devising of molding processes in which such pulp can be conveniently handled, both in the formation of the original molded blank in its compacting prior to induration, and in the final shaping and further compacting of the walls of such blanks.

As an example of the best method at present known to me of carrying out my invention I would proceed as follows:

I preferably take soft cotton rags, such as have been frequently laundered, as the laundering has already removed some of the objectionable gums originally present in the cotton, and turn them into pulp by digesting them in a solution containing about 5 percent of caustic soda (sodium hydrate, NaOI-I) and about 3 percent of soda (sodium carbonate, Na CO lOH O) for about four hours under an atmospheric pressure of from 30 to 50 pounds per square inch. This solution is about 50 percent stronger than that usually employed -in making paper pulp. The resultant pulp is consequently of a finer structure, more nearly homogeneous, and contains less gum and similar impuritiesthan does ordinary paper pulp. Consequently it has greater power of-absorption. I then mold suitable masses of this pulp into cup-shaped bodies or other forms of dimensions large enough to allow for the ultimate shrinkage that will occur in the drying and indurating steps of the process, by depositing a layer of the ulp preferably on the inside of a perforated metal former having side walls slightly tapering, like a cone, to a degree such that the cup-shaped mass thus deposited therein can be easily freed therefrom when partially dried. One degree of inclination.

is suflicient to free a cup two inches deep. A lesser inclination will serve for deeper cups. The. walls of these blanks may be partially compacted by pressure in the original mold or former while still wet and then allowed to dry sufiiciently to be removed from the former. In some cases they can be shaken out of the mold before drying as the fiber is felted together sufliciently to make them self-sustaining. The blanks are then further dried and subjected to compression in molds to compact the walls and expel the air trapped therein, indurated and finally molded into the desired exact shapes having the desired dimensions in any convenient way.

The process of forming or molding the pulp into the original blank may be carried out according to any of the well-known methods, as by pouring as well as by sucking the pulp into a perforated metal former of the desired shape.

The induration of the fiber in the blankmay also be carried out in the usual way byiinmersion in'a proper bath of zinc chloride, or the solution described in my pending application Serial No. 697,955, filed March 8,

. market so far as I know.

1924, allowed November 24, 1926, with subsequent washings in progressively weakening baths of the same solution-and ultimate washing out in pure water. The impregnated blank may be then, after curing, given its final shape and compactness of wall by compression in any suitable finishing dies.

While the best results are secured by using old cotton rags for making the pulp, a product useful for some purposes may be obtained when other forms of cellulose are substituted.

The main advantage of the invention lies in the successful production of a box, cu or other article having walls of indurated iber of integral, homogeneous structure, more than .040 inches in thickness, and up to an eighth of an inch and more in thickness, a thing which has not been heretofore in existence, so far as known to me. Boxes and structures for the uses for which the product of my invention is designed have been made usually heretofore of strips of paper and pasteboa-rd glued together. Such gluing cannot be easily done with indurated fiber, and consequently no boxes or similar receptacles of in durated fiber have heretofore been put on the As indurated fiber is much stronger than pasteboard and capable of receiving more elaborate ornamentation and artistic finish, the advances both in utility and beauty rendered possible by my invention are obvious.

The commercial use of indurated fiber has heretofore been limited to shapes which could be produced by slightly molding sheets, strips or tubes of that material under heat and pressure. The building-up of such laminated sheet or tube, and its subsequent molding under progressive operations by heat and pressure, have been costly and limited in scope. A

I am aware that various articles such as pails, bottles, barrels, etc. have been made by flowing paper pulp into molds with perforated walls, and allowing the fiber mass so deposited to dry, but none of these articles was indurated, and the blanks so formed were not further molded after drying, nor were their walls compacted by die pressure, so far as I am aware.

Having described my invention, I claim:

1. The process of making molded integral shapes of indurated fiber which comprises the following steps: Digesting a pulp' formed from old cotton cloth in an aqueous solution containing about 5 percent of sodium hydrate and about 3 percent of sodium carbonate for about four hours and under a pressure of from 30 to pounds to the square inch; forming a blank out of said pulp by flowing it into a mold having perforated walls through which is removed a major portion of its water content; drying said blank and impregnating it with an indurating liquid, and finally comshapes of indurated fiber which comprises the following steps: Digesting a pulp formed from old cotton cloth in an aqueous solution containing about 5 percent of sodium hydrate and-about 3 percent of sodium carbonate for about four hours and under a pressure of from 30 to 50 pounds to the square inch:

forming a blank out of said pulp by flowing it into a mold having perforated walls through which is removed a major portion of its water vcontent; drying said blank, compacting it by pressure to expel any entrapped air, impregnating it with an indurating liquid, and fur-' ther compacting and shaping the walls of said indurated blank by molding under pressure in suitable dies,

3. The herein described process which comprises digesting fibrous cellulose in a pulpmaking solution of such strength, under such pressure and during such period of time that the resulting pulp, when concentrated, dried and compacted, will form a mass suiriciently hygroscopic to permit an indurating zinc chloride solution to penetrate to a depth of more than twenty thousandths (.020) of an inch from its surfaces; shaping the pulped fiber so obtained in any desired form having walls more than forty thousandths .040) but not substantially exceeding one eighth of an inch in thickness by depositing it on a foraminous mold, sufliciently compacting the mass under pressure to expel substantially all entrapped air,-and impregnating the blank so obtained with a suitableindurating solution,

such as one containing zinc chloride.

HORACE H. CLARK. 

